Photochemical process



W. 0. SNELLING.

PHOTOCHEMICAL PROCESS.

APPLlcATloN FILED MAR.6.1911.

194%@984-6 Patented Jne 209 w22.

JVITNESSES 1 ATTORN EY WALTER O. SNELLING, 0F ALLENTOWN, PENNSYLVANIA4 PHOTOCHEMICAL PROCESS.

Specicationpof Letters Patent. latnted June 20, 1922 Application tiled March 6, 1917. Serial No. 152,589.

To all whom t may concern.' n

Be it known that I, WALTER O. SNELLING, a citizen of the United States, and a resident of Allentown, in the county of Lehigh and State of Pennsylvania, ha've linvented a new and useful Improvement in Photochemical Processes, of which the following is a specification.

My invention relatesy to chemical reactions which involve the exposure of mix tures of liquid or gaseous reagents to actinic lightfor the purpose of inducing or facilitating their interaction, and itis my object to provide a simple and rapid process for performing such reactions in an economical manner and upon a commercial scale. One specific object of my invention is to prepare halogenated carbon compounds by photochemical reaction between hydrocarbons and halogens, and, in particular, to continuously produce carbon tetrachlorid, chloroform, methylene chlorid and other chlorine substitution products of methane and other hydrocarbons with which chlorine forms mixtures that tend to react with explosive violence under the influence of actinio light.

The single gure of the accompanying drawing is a central vertical sectional view of a reaction cell suitable for carrying out the process of my present invention.

In View of the highly explosive nature of Vgas mixtures composed of halogens, p arand halogen-combining ticularly chlorine,

hydrogen, methane and substances such as other hydrocarbons of the methane series,

it has heretofore been thought necessary, in bringing about direct combination of such substances, to take precautions against explosion by exposinglthe reaction mixture to diffused light only, orby making use of reaction vessels in the form of slender tubes an inch or less in diameter and thereby conducting away the heat developed in the reaction fast enough to prevent the reaction mixture from becoming heated to the ignition point. If diffused light is employed, the reaction proceeds very slowly, while the forms of apparatus in which slender tubes are used are of small capacity. For these reasons, it has not heretofore been found practicable to produce halo-l genated compounds by direct photochemical combination upon any considerable scale without making use of va very large numberof small-capacity units or cells or employing speclal means for preventing the full rays of the light source from falling upon the reacting gases or vapors.

My .present process results from the disc'overy that, under the conditions to be fully describedfbelow, highly explosive gas mlxtures such as mixtures -of chlorine and methane can be introducedl into large glass vessels and exposed to intense light, even to the direct rays of the sun or of intensely actinic iiaming arcs or mercury vapor lamps, without explosion and with rapld production of halogen substitution products.. I obtain this result, in general, by contlnuously introducing the gases or vapors which I desire to combine'into a reaction chamber in which currents of gas are always maintained in rapid motion, such gas currents having the effect of transferrmg to the walls of the container much of the heat liberated by the reaction and thereby mamtammg the temparature within the react1on chamber safely below the ignition lpolnt. In one specific method of carrymg out my process, I introduce the reaction mixture from below into a dome-shaped transparent vessel exposed directly to a source efactinic light. Each portion of gas, as it enters the vessel and l1s exposed to the actinic rays from the external source, reacts and liberates sufficient heat to render it much lighter than the surrounding gases. The heated gas therefore rises to the top of the container and becomes cooled and, denser by contact with the walls of. the vessel, whereupon it sinks rapidly along the outer walls, is partly withdrawn in the form of liquid and gaseous reaction products and is partly aspirated upward by the incoming gases, such cooled and aspirated portion of the reaction products serving to still further lessen the temperature of the gases remote from the walls of the'container. e

For a better understanding of my invention, reference may now be had to the accompanying drawing, ,which shows diagrammatioally the essential structural features of a reaction ycell in which my process may be performed. A dome-shaped vessel 1, ofl glass or other transparent material, 1s .shown resting upon a pan or tray 2, which `may be constructed of stoneware or of some other material which is not atl the domeis vio-crous and complete:

heat is liberatec since the reactions involved vwith the dome 1 completely fil The lamp 6 is turned on, and the reaction' 'necessary actinic rays, and an outlet 7 for liquid reaction products extends through the pan 2 at any convenient point.

r'Ihis form of apparatus may bestarted ed with air.

mixture consisting, for example, of three parts of chlorine and one part of methane or natural `as is introduced into the dome l through t ie 1nlet I I I creasing rate. If t e indicate( mixture of chlorine and methane is employed, and if the dome v1 is about two vfeet in diameter and five feet High, the gas mixture may be first introduced at the rate yof about one tenth of a cubic foot per minute, this rate beingv gradually increased for about one hour, at the end of which time the mixed chlorine and methane may be introduced at the rate of two'cubic feet per minute with complete' and quiet reaction between the gases. This rate of reaction is hundreds of times faster than that which is capable of attainment with any prior form of single cell Vof which I am aware. n I v At the beginning ofthe foregoing operation, the large amount of air present in the dome exerts a negative catalytic effect upon the chlorine and methane and prevents ini' tial explosions, which might otherwise ccur beforel the normal operation is established. s more and more of the reaction mixture is introduced, the air is gradually displaced until ultimately no air is present. As the amount of air in the dome decreases, the reaction between the chlorine and methane begins, proceedingslowly at first on ac.

count of the negative catal tic eilect ot the air,and increasing in rapi ity as the air 1s displaced, until finally the reaction Within are highly exotheimic, but the convection currents which are set up within ythe dome, as indicated by the arrows on the drawing, preventl the temperature' ofl the reactiig gases from risin to the ignition point. desired, the coo ing capacity of the dome walls may be increased by directing jets of air or water downwardly upon the dome.

Another factor which contributes to the quiet/operation of the illustrated form of device is the continuouspresence of a conpipe 3 at a radually in.

Muchy This Agas blanket is composed of gases inLV various degrees of combination, the gases adjacent tothe wall ofthe dome nearest the source of li ht bein composed of wholly combined ro ucts, an the degree of combination ecreasing toward the gas inlet.

The rays from the light source are therefore consumed progressively as the -pass throughthe dome to the gas inl t, t iis feature of the operation of m cell ing broadly describedand claime f in' my copending applications for Letters Patent, Serial N o. 776,834, filed July -1 1913, and Serial No. 848,355, med July 1, 1914.

My resent process is wholly distinct from the chlorination experiments which are reported in the literature andl in which mixtures of chlorine and hydrogen, methane or the like have been exposed to light in large vessels to'jbringn about their reaction. In all of such prior experiments, the vessels have -irst been filled with the gas mixture and then exposed .to light, with the result that explosion occurs unless the light applied is very dim. In the latter case, the chlo'rinating` reaction roceeds at a rate which is of an ordero magnitude entirely different from that vwhich characterizes my process. The prior experiments in which dim light has been-fused have required eight or ten hoursj exposurel to the light in order to bring about complete reaction in a few liters of gas, whilev my process is capable ot'y producing .complete reaction -in similar gas mixtures at the rate'o'f about sixty liters per minute, or one liter.A per second, a rate which indicates that my reaction proceeds many thousands of times as rapidly as lthe reactions taking placein the prior processes in which dim light is necessarily employed.

I believe 'thatfI--am tliewirst to produce continuous and quiet reactions 'in explosive gas mixtures byV continuously introducing such a mixture into a large reaction chamber, as opposed to a slender tube, the rear tion chamber ,being exposed to bright light. It is therefore to be understood that my invention is not restricted to the use of any particular form of apparatus, or to the treatment of any speciic mixtures of reagents, and no limitations are to be imposed upon Vmy invention except such as are indicated inthe appended claims.

I claim as-my invention:

1. The process which comprises producingr movement within a body of hotochemically reactive fluid by heat resulting from exposing the fluid to actinic rays.

2. The process which comprises circulating a body of photochemically reactive Huid by the action of actinic rays.

3. The processV which comprises circulating-a body of photochemically'reactive fluid adj acent-to a cooling surface by the action of actinic rays.

4:. The process which comprises circulating a body of photochemically reactive fiuid adjacent to a cooling surface by the action of actinic rays, and continuously introducing fresh fluid.

5. The process which comprises exposing a body of photochemically reactive fluid of exothermic nature to 'actinic rays, and utilizing the heat of reaction to cause the iiuid to move adjacent to a cooling surface.

6. The process Which comprises reducing the density of a portion of' a photochemically reactive fluid of exothermic nature by exposing such fluid to actinic rays until its temperature has increased, and causing such portion of photochemically reactive fluid to then displace denser li-uid adjacent to' a cooling surface.

7. The process which comprises continuously introducing a mixture of photochemically reactive gases or vapors into a reaction chamber exposed directly to a source of actinic rays, and maintaining the temperature Within the said chamber below the ignition point of the introduced material by means ously introducing a photochemically reactive fluid into a reaction chamber exposed to actinic rays, and maintaining the temperature Within the chamber belowthe point of ignition of the liuid by continuously circulating the fluid adjacent to a cooling surface by means oi convection currents Within the fluid.

In testimony whereof, I have hereunto subscribed my name this 2nd day of March WALTER O. SN ELLING.

l il 

